This invention relates to an apparatus for locating the source of electromagnetic noise radiation, and more particularly to such an apparatus for determining the location of sparking in electrical equipment.
Electrical arcs or sparking gaps constitute a prevalent source of radio interference or noise. Typical of such sources are the sparking of the brushes in an electric motor, of defective contacts in an electric switch, of automobile ignition systems and of loose hardward on an electric utility pole.
The electromagnetic fields generated by such sparking are characterized as bursts of radiated energy consisting of a very broad band of radio frequencies and each burst having a fast rise time, typically being on the order of a nanosecond.
Radio noise-source locators of the prior art are comprised of a radio receiver that is tunable to one frequency (or to one narrow band of frequencies) at a time. This tunable feature makes it possible to sense electromagnetic noise of all kinds ranging from single frequency continuous wave signals to very broad band or white noise, either or which may or may not be modulated. One such noise source locator is described in U.S. Pat. No. 3,965,425 issued June 22, 1976 and assigned to the same assignee as the present invention.
Although such noise source locators of the prior art are capable of sensing electrical sparking, they do so by sensing only a small portion of the broad spectrum of frequencies radiated. Many stages of signal amplification are thus usually required to produce a usable indication of broad band sources (e.g. RF, IF and audio amplifier stages). Furthermore the receiver must be tuned away from other sources of noise such as local radio or television stations. Such locators thus tend to be large, complex and costly in addition to requiring a trained operator in their use.
It is accordingly an object of the present invention to provide a simple low cost apparatus capable of selectively sensing radiated fields from electrical arcs.
It is a further object of this invention to provide such a locator that senses a broad frequency spectrum of radiated noise and requires no tuning.
It is a further object of the present invention to provide such a locator that is insensitive to continuous wave signals such as those generated by television and radio stations.
It is yet a further object of this invention to provide an electromagnetic noise source locator that is selectively responsive to sparking.